1. Field of the Invention
The present invention relates to an apparatus for determining the characteristics of particles suspended in a liquid.
2. Description of the Related Art
The Coulter method is known, inter alia, for determining the number, size distribution and electrokinetic mobility of particles suspended in a liquid. This method was described in DE-AS 2,053,825. A conductance measuring cell in the form of a fine single pore or a capillary is used therein for this purpose. The diameter of such a cell or capillary is always larger than the particle, and its cross-section is uniform over its length. The funnel-shaped inlet zones connected upstream and downstream from the cell have an even larger cross-section and serve to preliminarily position the particles at the center of the pore. The particles are transported through the measuring pore by the flowing liquid or by means of an electric voltage drop. The change in resistance in the liquid during the passage of the particles through the measuring pore furnishes a measure of the particle volume or its mobility. The measuring capillaries in the Coulter apparatus have a diameter of about 70-100 microns. Moreover, the deformability of red blood corpuscles is quantized from a measurement of their passage through an unstructured channel of the same diameter or, more precisely, the same cross-section, as the channel having a smaller cross-section than the cross-section of the blood corpuscles.
The prior art methods for measuring either the number, volume, electrokinetic mobility or deformability of particles, all employ a cylindrical channel having a constant cross-section as the actual measuring zone. With such type of uniformly configured capillary, the information provided by the measuring method is limited, however, to merely the deformability of the particle.
Accordingly, based on the described state of the art, there is still a need for a device in which volume, as well as deformability and other characteristics, may be determined in a single passage through one and the same measuring channel which can avoid the drawbacks of the prior art devices, such as avoidance of field distortion at the inlet and outlet resulting from improved impingement conditions at the actual measuring pore, avoidance of the occurrence of non-axial particle paths and avoidance of cyclically returning particles in larger pore cross-sections.